Abstract
Abstract. Recovery of photosynthesis and transpiration is strongly restricted by low temperatures in air and/or soil during the transition period from winter to spring in boreal zones. The extent to which air temperature (Ta) and soil temperature (Ts) influence the seasonality of photosynthesis and transpiration of a boreal spruce ecosystem was investigated using a process-based ecosystem model (CoupModel) together with eddy covariance (EC) data from one eddy flux tower and nearby soil measurements at Knottåsen, Sweden. A Monte Carlo-based uncertainty method (GLUE) provided prior and posterior distributions of simulations representing a wide range of soil conditions and performance indicators. The simulated results showed sufficient flexibility to predict the measured cold and warm Ts in the moist and dry plots around the eddy flux tower. Moreover, the model presented a general ability to describe both biotic and abiotic processes for the Norway spruce stand. The dynamics of sensible heat fluxes were well described by the corresponding latent heat fluxes and net ecosystem exchange of CO2. The parameter ranges obtained are probably valid to represent regional characteristics of boreal conifer forests, but were not easy to constrain to a smaller range than that produced by the assumed prior distributions. Finally, neglecting the soil temperature response function resulted in fewer behavioural models and probably more compensatory errors in other response functions for regulating the seasonality of ecosystem fluxes.
Highlights
Forests in boreal areas are likely to be considerably influenced by climate change, elevated CO2 and management (Schroter et al, 2005; Boisvenue and Running, 2006; Jansson et al, 2008)
The results suggested that inhibition of photosynthesis and transpiration due to low soil temperature needs to be considered in the model when there is a large delay between cumulative air temperature (Ta) and soil temperature (Ts) in spring
The mean annual precipitation was 588, 533 and 512 mm in 2001, 2002 and 2003, respectively, which is lower than the 30-yr mean annual precipitation of 613 mm
Summary
Forests in boreal areas are likely to be considerably influenced by climate change, elevated CO2 and management (Schroter et al, 2005; Boisvenue and Running, 2006; Jansson et al, 2008). Understanding the interaction between ecosystem processes and historical climate conditions is fundamental to predicting how the ecosystem will be affected by environmental changes. In boreal conifer forests, the climate both aboveground and belowground regulates photosynthesis and transpiration processes (Suni et al, 2003; Mellander et al, 2008). Recovery of photosynthesis and transpiration is strongly restricted by low temperatures in air and/or soil during the transition period from winter to spring (Makelaet al., 2004; Mellander et al, 2006; Ensiminger et al, 2008; Wu et al, 2011, 2012). Photosynthesis recovery in spring varies annually, which is probably caused by both atmospheric and soil conditions. The atmospheric conditions will sometime create a high requirement for transpiration and photosynthesis when the plant is not fully adapted to high light intensity or high air temperature while the soil is still very cold
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